[rescue] Creating/Simulating/Emulating an old 1970s Bell Telephone Network

Matthew Haas wedge at lightlink.com
Mon Aug 15 23:08:27 CDT 2005

On Mon, 15 Aug 2005, James Fogg wrote:
> >  I'm wondering if anyone has information or pointers
> > regarding the above-mentioned topic. I'm teaching a
> > Data/Voice Communications course this fall, and in my efforts
> > to convey some deeper understanding of communications (plus
> > expose these students to things like modems, rotary phones,
> > even have the opportunity to try out classic coloured box phone
> > phreaking) I was brainstorming in this area.
> If you want to duplicate the actual Bell system, you have to span
> several tiers (long lines, exchanges, etc.) and several generations of
> electronics (or mechanics in the case of Strowger switches). It would be
> daunting.

 I'm hoping for a close approximation at this point.. not to necessarily
have a museum-like replica. Where convenient, some functionality may be
replaced by ICs and breadboard digital logic solutions (which is why I'm
looking for a combination of recreation and simulation.. to knock the
daunting factor down a couple notches... I've got an individual with EE
experience hooked on the idea too and he's already got his mind humming
with ideas of implementation).

> >  I'm looking at eventually implementing the CO, switches, and
> > end devices (be it an off-the-shelf phone, mock-up payphone,
> > or whatnot).. and to intentionally make it operate on
> > frequencies, so it can be manipulated...
> You could acquire an old switch like a Siemens hybrid or a modern AT&T
> 5ESS with SS7 protocol. But it would be much simpler to find an old PBX
> or key system that supports type 500/2500 phones (POTS phones). There
> are many Stromberg-Carlson small exchange switches around too.

 I've got access to a smaller PBX (supports something like 16 phones..
analog).. And I've stumbled upon the 4ESS or 5ESS, so I'll look into their
functionality a bit further.

 The idea is to have a system that can handle something in the range of
2-8 phones... enough to create some configuration scenarios (like
exchange dialing) yet hopefully not as mechanically cumbersome. Basically
the 70s phone network with some benefits of modern technology.

> >  Any recommendations? Web sites, books? I figure this will be
> > as much a learning experience for me as it will for my students.
> The web. It's well documented.
> http://www.att.com/history/
> You could also build simple phones from carbon mics, simple earpieces
> and batteries. Add a switchboard for routing, then maybe add a strowger
> and dials. The facinating thing about the phone system is that the first
> phones with dials (early 1930's) are still supported. That is why you
> can dial the operator by pressing the switch-hook 10 times quickly.

 Thanks for the pointers! I'll definitely be exploring the
phone-from-scratch idea.


 Matthew Haas
 Corning/Watkins Glen, NY

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